I don't believe in monolithic aliens who all talk exactly alike,with the same accents, any more than I believe in humans who all talkexactly alike. Hence, the difference between Vir and Londo.

When they're together in their quarters, they're talking in Centauri,which we hear as English, as in WW II movies, the Germans are obviouslytalking to each other in German, but we hear it in English. (The onlyother alternative is to subtitle whole lengthy segments of the show, whichis both unworkable, awkward, and unfair to blind viewers.)